Two types of thermostatically controlled mixing valves are generally employed in sanitary installations. One type, hereinafter referred to as an individual thermostat, includes a volume regulating assembly which functions as a shut-off valve that opens and closes the hot and cold water supply to the valve and also controls the temperature discharge of the water. The other type, hereinafter referred to as a central thermostat, includes only a temperature regulating mechanism with automatic one way valve means which prevents the back flow of hot and cold water through the potable water system. The valve for opening and closing the temperature regulated water passing through the mixing valve is located at or near a use point. Thermostatically controlled mixing valves of the type described are published in German Patent Applications p 23 55 100.0 published May 15, 1975 and p 23 55 101.1 published May 15, 1975.
Individual thermostats differ from central thermostats in that the temperature and volume of the water can be adjusted by a volume control assembly mounted within the valve body whereas in the central thermostat, only the temperature of the water can be adjusted. The desired volume of water passing through a central thermostat is adjusted by means of separate shut-off valves provided at one or more of the use points.
One of the disadvantages of thermostatically controlled mixing valves of either the individual or the central types is that the essential elements of one mixing valve type cannot be combined with the essential elements of the other type. Also, it is not possible, for example, to rebuild a mixing valve of the central thermostat type into mixing valve of the individual type without replacing the entire thermostatically controlled mixing valve.